Department of Electrical and Computer Engineering, University of Toronto, Toronto, Ontario M5S 3G4, Canada.
ACS Nano. 2013 Jul 23;7(7):6111-6. doi: 10.1021/nn401918d. Epub 2013 Jun 7.
Colloidal quantum dot (CQD) solar cells combine solution-processability with quantum-size-effect tunability for low-cost harvesting of the sun's broad visible and infrared spectrum. The highest-performing colloidal quantum dot solar cells have, to date, relied on a depleted-heterojunction architecture in which an n-type transparent metal oxide such as TiO2 induces a depletion region in the p-type CQD solid. These devices have, until now, been limited by a modest depletion region depth produced in the CQD solid owing to limitations in the doping available in TiO2. Herein we report a new device geometry-one based on a donor-supply electrode (DSE)-that leads to record-performing CQD photovoltaic devices. Only by employing this new charge-extracting approach do we deepen the depletion region in the CQD solid and thereby extract notably more photocarriers, the key element in achieving record photocurrent and device performance. With the use of optoelectronic modeling corroborated by experiment, we develop the guidelines for building a superior CQD solar cell based on the DSE concept. We confirm that using a shallow-work-function terminal electrode is essential to producing improved charge extraction and enhanced performance.
胶体量子点 (CQD) 太阳能电池将溶液处理能力与量子尺寸效应可调性相结合，可实现低成本地收集太阳的宽可见光谱和红外光谱。迄今为止，性能最高的胶体量子点太阳能电池依赖于耗尽型异质结结构，其中 n 型透明金属氧化物（如 TiO2）在 p 型 CQD 固体中诱导耗尽区。由于 TiO2 中可用掺杂的限制，这些器件迄今为止一直受到 CQD 固体中产生的适度耗尽区深度的限制。在此，我们报告了一种新的器件几何形状——基于施主供应电极 (DSE)——它导致创纪录的 CQD 光伏器件性能。只有采用这种新的电荷提取方法，我们才能加深 CQD 固体中的耗尽区，从而提取出明显更多的光生载流子，这是实现创纪录的光电流和器件性能的关键因素。通过光电建模与实验的佐证，我们为基于 DSE 概念构建优越的 CQD 太阳能电池制定了指导方针。我们证实，使用低功函数终端电极对于产生改进的电荷提取和增强的性能至关重要。
